This disclosure relates to thermoplastic polyester compositions and methods for the manufacture thereof, and in particular to blends of polyesters and polyetherimides useful in the manufacture of containers.
Plastic containers, particularly those useful for the containment of liquids, can be made from a variety of thermoplastic polymers, although individual thermoplastic polymers have certain drawbacks. Polyetherimide and polycarbonate compositions, for example, exhibit a high level of oxygen permeability (Encyclopedia of Polymer Science and Technology, N. M. Bikales, Vol. 9, 316-327, Wiley, New York (1965); Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., M. Grayson, Vol. 3, 480-502 (1978), such that these resins are not practical for applications requiring low oxygen permeability. Thus, while these resins are suitable for use as large size soda bottles, for example, the leak rates are not optimal for smaller size bottles, or for liquids such as beer, which is more sensitive to oxygen and other gases. Multi-layer bottles can be used in order to provide the necessary sealing, but are more expensive and time-consuming to manufacture. Polyester resins have also been used as plastic containers for liquids, but frequently exhibit undesirably high levels of creep, resulting in permanent deformation.
Blends of the foregoing polymers are known. For example, U.S. Pat. No. 4,141,927 discloses a blend of polyetherimide with polyester to lower the melt viscosity of the polyetherimide. U.S. Pat. No. 4,259,458 discloses a blend a polyester and at least one thermoplastic polymer such as a polycarbonate, a styrene resin, an alkyl acrylate resin, a polyurethane, a vinyl chloride polymer, a poly(aryl ether), a copolyetherester block polymer, or a polyhydroxyether. While useful, manufacture and molding of such blends can be difficult, especially when a large proportion of polyester is used. There accordingly remains a need in the art for improved thermoplastic resin compositions and efficient methods for the manufacture of such compositions.